Conductive routings in integrated circuits using under bump metallization

ABSTRACT

An integrated circuit structure includes a first conductive layer and an under bump metallization layer over the first conductive layer. The first conductive layer has a first conductive region and a second conductive region electrically isolated from the first conductive region. The under bump metallization layer has a first conductive area and a second conductive area electrically isolated from the first conductive area, the first conductive area substantially located over the first conductive region and the second conductive area substantially located over the second conductive region. At least one of the first conductive area or the first conductive region includes a first protrusion extending toward the second conductive area or second conductive region, respectively. Conductive vias connect the first conductive region to the second conductive area and connect the second conductive region to the first conductive area, and the vias include at least one via connected to the first protrusion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 13/454,968, filed Apr. 24, 2012, which claims priority to and is a continuation of U.S. patent application Ser. No. 12/343,261, filed Dec. 23, 2008, which claims priority to U.S. Provisional Application Ser. No. 61/017,139, filed on Dec. 27, 2007, the entire disclosures of which are incorporated by reference.

TECHNICAL FIELD

The present invention relates generally to conductive routings in integrated circuits, and in one aspect, to conductive routings in integrated circuits used as power switches.

BACKGROUND

Integrated circuits (“IC”), which generally refer to electronic circuits formed on a silicon or other semiconductor substrate, have widespread application in modern electronic systems. An IC chip may contain circuit devices, such as transistors, and electrical interconnects to electrically couple the circuit devices. An outer surface of the IC chip may also contain conductive pads for providing electrical coupling of the chip to external devices, such as voltage sources and control circuits. Traditionally, electrical connection between the transistors in the semiconductive substrate and the conductive pads is accomplished through the use of multiple conductive layers that are formed over the semiconducting substrate of the integrated circuit chip but below an insulative layer that supports the conductive pads (an aperture in the insulative layer can provide electrical coupling of the contact pad to the uppermost conductive layer). For example, an integrated circuit chip may have metal lines and vias that electrically couple the source and drain regions of the transistors to the conducting pads of the integrated circuit chip.

Voltage regulators, such as DC to DC converters, are used to provide stable voltage sources for electronic systems. Switching voltage regulators are known to be an efficient type of DC to DC converter. Such voltage regulators typically include a power switch to generate a rectangular-wave voltage that is filtered to provide the output DC voltage.

Conventionally, the power switch was fabricated as an integrated circuit chip with wire bond packaging. More recently, the power switch has been fabricated as an integrated circuit chip with flip-chip packaging (in which solder bumps are placed on the top surface of the chip, and the chip is mounted upside down with the solder bumps connected directly to a printed circuit board, interposer, or to a package).

SUMMARY

In one aspect, an integrated circuit structure includes a first conductive layer and an under bump metallization layer over the first conductive layer. The first conductive layer has a first conductive region and a second conductive region electrically isolated from the first conductive region. The under bump metallization layer has a first conductive area and a second conductive area electrically isolated from the first conductive area, the first conductive area substantially located over the first conductive region and the second conductive area substantially located over the second conductive region. At least one of the first conductive area or the first conductive region includes a first protrusion extending toward the second conductive area or second conductive region, respectively. Conductive vias connect the first conductive region to the second conductive area and connect the second conductive region to the first conductive area, and the conductive vias include at least one via connected to the first protrusion.

Implementations can include one or more of the following features. The first conductive area may include the first protrusion extending toward the second conductive area. The first conductive region may include a second protrusion extending toward the second conductive region, and the conductive vias may include at least one via connected to the second protrusion. The first conductive region may include the first protrusion extending toward the second conductive region. A first flip-chip interconnect may be on the first conductive area of the under bump metallization layer, and a second flip-chip interconnect may be on the second conductive area of the under bump metallization layer. The first flip-chip interconnect and second flip-chip interconnect may be solder bumps, solder balls, copper pillars or stud bumps. The first conductive region may have a plurality of first protrusions extending toward the second conductive region, and the second conductive region may have a plurality of second protrusions extending toward the first conductive region. The first conductive area may have a plurality of third protrusions extending toward the second conductive area, and the second conductive area may have a plurality of fourth protrusions extending toward the first conductive area. A plurality of first conductive vias may connect the plurality of first protrusions to the plurality of fourth protrusions, and a plurality of second conductive vias may connect the plurality of second protrusions to the plurality of third protrusions. The first conductive area may have a plurality of first protrusions extending toward the second conductive area, and the second conductive area may have a plurality of second protrusions extending toward the first conductive area.

The under bump metallization may include a contact layer to contact a portion of the first conductive layer and an outer layer. An intermediate layer may be between the contact layer and the outer layer. The intermediate layer may include a diffusion-blocking material. The contact layer may include aluminum, the intermediate layer may include a nickel vanadium alloy, and the outer layer may include copper. The contact layer may be titanium and the outer layer may be copper. The outer layer may be a metal layer, e.g., copper, having a thickness greater than 6 microns.

The integrated circuit structure may further comprise a substrate under the first conductive layer. The substrate may have a first distributed transistor with a first plurality of doped source regions and a first plurality of doped drain regions, and the first conductive region and the second conductive area may be electrically coupled to the first plurality of doped source regions and the second conductive region and the first conductive area may be electrically coupled to the first plurality of doped drain regions. The first plurality of doped source regions and the first plurality of doped drain regions may be are arranged in an alternating pattern in the substrate. The substrate may have a second distributed transistor with a second plurality of doped source regions and a second plurality of doped drain regions arranged in an alternating pattern in the substrate. The first conductive layer may have a third conductive region and a fourth conductive region electrically isolated from the third conductive region. The under bump metallization layer may have a third conductive area and a fourth conductive area electrically isolated from the third conductive area, the third conductive area substantially located over the third conductive region and the second conductive area substantially located over the fourth conductive region. At least one of the third conductive area or the third conductive region may include a second protrusion extending toward the fourth conductive area or fourth conductive region, respectively. The conductive vias may connect the third conductive region to the fourth conductive area and connect the fourth conductive region to the third conductive area. The conductive vias may include at least one via connected to the second protrusion. The third conductive region and the fourth conductive may be electrically coupled to the second plurality of doped source regions and the fourth conductive region and the third conductive area electrically coupled to the second plurality of doped drain regions. The first conductive area may be electrically coupled to the third conductive area. The first conductive area may be electrically coupled to the fourth conductive area. Thee second conductive area may be electrically coupled to the fourth conductive area.

A second conductive layer may be between the first conductive layer and the substrate. The second conductive layer may include a plurality of first conductive portions and a plurality of second conductive portions disposed below the first conductive region, and may include plurality of third conductive portions and a plurality of fourth conductive portions disposed below the first conductive region. A third plurality of vias may connect the first conductive region to the plurality of first conductive portions, and a fourth plurality of vias may connect the second conductive region to the plurality of third conductive portions. A fifth plurality of vias may connect the first conductive area to the plurality of second conductive portions, and a sixth plurality of vias may connect the second conductive area to the plurality of fourth conductive portions. A first flip-chip interconnect may be on the first conductive area of the under bump metallization layer, a second flip-chip interconnect may be on the second conductive area of the under bump metallization layer, a third flip-chip interconnect may be on the third conductive area of the under bump metallization layer, and a fourth flip-chip interconnect may be on the fourth conductive area of the under bump metallization layer.

In another aspect, an integrated circuit structure includes a first conductive layer and a second conductive layer over the first conductive layer. The first conductive layer has a first conductive region and a second conductive region electrically isolated from the first conductive region. The second conductive layer has a first conductive area and a second conductive area electrically isolated from the first conductive area, the first conductive area substantially located over the first conductive region and the second conductive area substantially located over the second conductive region. Only one of the first conductive area or the first conductive region includes a first protrusion extending toward the second conductive area or second conductive region, respectively. Conductive vias connect the first conductive region to the second conductive area and connect the second conductive region to the first conductive area. The conductive vias include at least one via connected to the first protrusion.

Implementations can include one or more of the following features. The first conductive area may include the first protrusion extending toward the second conductive area. The first conductive region may include the first protrusion extending toward the second conductive region. The first conductive region may have a plurality of first protrusions extending toward the second conductive region, and the second conductive region may have a plurality of second protrusions extending toward the first conductive region. The first conductive area may have a plurality of third protrusions extending toward the second conductive area, and the second conductive area may have a plurality of fourth protrusions extending toward the first conductive area. A plurality of first conductive vias may connect the plurality of first protrusions to the plurality of fourth protrusions, and a plurality of second conductive vias may connect the plurality of second protrusions to the plurality of third protrusions. The first conductive area may have a plurality of first protrusions extending toward the second conductive area, and the second conductive area may have a plurality of second protrusions extending toward the first conductive area. The integrated circuit structure may include a substrate under the first conductive layer. The substrate may have a first plurality of doped source regions and a second plurality of doped drain regions, and the first conductive region and the second conductive area may be electrically coupled to the first plurality of doped source regions and the second conductive region and the first conductive area may be electrically coupled to the first plurality of doped drain regions.

In another aspect, an integrated circuit structure includes a first conductive layer, a second conductive layer under the first conductive layer, and an under bump metallization layer over the first conductive layer. The first conductive layer has a first conductive region and a second conductive region electrically isolated from the first conductive region. The second conductive layer includes a first conductive portion and a second conductive portion electrically isolated from the first conductive portion, the first conductive portion disposed below the first conductive region, the second conductive portion disposed below the second conductive region. The under bump metallization layer has a first conductive area and a second conductive area electrically isolated from the first conductive area, the first conductive area substantially located over the first conductive region and the second conductive area substantially located over the second conductive region. A first conductive via connects the first conductive area to the first conductive portion. The first conductive via passes through an aperture in and is electrically isolated from the first conductive region. Conductive vias connect the first conductive region to the second conductive area, connect the second conductive region to the first conductive area, connect the first conductive portion to the second conductive region, and connect the second conductive portion to the first conductive region.

Implementations can include one or more of the following features. A second conductive via may connect the second conductive area to the second conductive portion. The second conductive via may pass through an aperture in and be electrically isolated from the second conductive region.

In another aspect, an integrated circuit structure includes a first conductive layer, a second conductive layer under the first conductive layer, and an under bump metallization layer over the first conductive layer. The first conductive layer has a first conductive region and a second conductive region electrically isolated from the first conductive region. The second conductive layer has a first conductive portion and a second conductive portion electrically isolated from the first conductive portion, the first conductive portion disposed below and substantially overlapping the first conductive region, the second conductive portion disposed below and substantially overlapping the second conductive region. The under bump metallization layer has a first conductive area and a second conductive area electrically isolated from the first conductive area, the first conductive area disposed over and substantially overlapping the first conductive region and the second conductive area disposed over the second conductive region. At least one of the first conductive area, first conductive region or first conductive portion includes a protrusion extending toward the second conductive region, second conductive area or second conductive portion, respectively. Conductive vias connect the first conductive region to the second conductive area, connect the second conductive region to the first conductive area, connect the first conductive portion to the second conductive region, and connect the second conductive portion to the first conductive region. The conductive vias including at least one via connected to the protrusion.

In another aspect, an integrated circuit structure includes a first conducive layer and an under bump metallization layer over the first conductive layer. The first conductive layer has a first conductive region and a second conductive region electrically isolated from the first conductive region, the first conductive region having a first protrusion extending toward the second conductive region. The under bump metallization layer has a first conductive area and a second conductive area electrically isolated from the first conductive area. The first conductive area is substantially located over the first conductive region and the second conductive area is substantially located over the second conductive region. The first conductive area has a second protrusion extending toward the second conductive area. A first conductive via connects the first protrusion to the second conductive area, and a second conductive via connects the second protrusion to the second conductive region.

Advantages may include the following. The lengths of conductive routings from doped regions in a substrate to conducting pads can be shortened. Interconnection resistance and power loss can be reduced. In addition, the conductive routing structure of the present invention can permit planar current flow so as to reduce resistance and current flow density, thereby increasing the reliability of circuits and devices. The area needed for providing conducting pads on an IC chip can be reduced. As a result, a chip implemented with the present invention can have cheaper dies in a smaller package, lower power loss, and shorter conductive path lengths than a traditional IC structure. The area available for functional devices in a chip, therefore, can be increased. At the same time, the performance of devices and circuits on a chip can be increased as a result of reduced resistance and power loss.

The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic exploded perspective view of an integrated circuit structure with under-bump metallization and a distributed transistor fabricated in a checkerboard pattern.

FIG. 2 is a schematic cross-sectional view of the integrated circuit structure of FIG. 1 illustrating a single source-drain pair.

FIG. 3 is a schematic plan view of a portion of the substrate from FIG. 1.

FIG. 4 is a schematic perspective view of a conductive area from the second conductive layer from the integrated circuit structure of FIG. 1.

FIG. 5 is schematic plan view of the under-bump metallization layer with the solder bump shown in phantom.

FIG. 6 is a schematic cross-sectional view of the uppermost conductive layer and the under-bump metallization.

FIG. 7 is a schematic circuit diagram of the integrated circuit structure of FIG. 1.

FIG. 8 is a schematic top view illustrating multiple adjacent under bump metallization areas arranged in a checkerboard pattern.

FIG. 9 is a schematic exploded perspective view of an integrated circuit structure with under-bump metallization and a distributed transistor fabricated in a pattern of parallel TOWS.

FIG. 10 is a schematic top view illustrating multiple adjacent under bump metallization areas arranged in parallel rows.

FIG. 11 is a block diagram of a switching regulator.

FIG. 12 is a circuit diagram illustrating electrical connections of an under-bump metallization layer.

DETAILED DESCRIPTION

FIGS. 1 and 2 illustrate one implementation of an integrated circuit structure 10 that can be used as a power switch. The structure 10 includes a substrate 20, a lowermost first conductive layer 30, a middle second conductive layer 40 over the first conductive layer 20, and a third conductive layer 50 over the second conductive layer 40. In addition, an under-bump metallization (UBM) layer 60, also termed a post-passivation metallization, is disposed over the third conductive layer 50 to provide electrical contact for a solder bump 80. The integrated circuit structure has a first insulation layer 70 between the first conductive layer 30 and the second conductive layer 40, a second insulation layer 72 between the second conductive layer 40 and the third conductive layer 50, and a third insulation layer 74, e.g., a passivation layer, between the third conductive layer 50 and the UBM layer 60. The first conductive layer 30 can be formed directly on the substrate 20, although portions of the first conductive layer will be separated from conductive lines formed on the substrate 20 by another insulating layer. The conductive layers can be formed of a metal, such as aluminum or copper, and the insulation layers can be formed of an oxide, such as silicon oxide, or a nitride.

Referring to FIGS. 1-3, the substrate 20 has a number of first doped regions 22 and a number of second doped regions 24 formed in, e.g., implanted into the surface layer of, a semiconductor substrate body 26, e.g., a silicon body. The first doped regions 22 and second doped regions 24 can be doped regions of a distributed transistor. In the illustrated implementation, the first doped regions 22 serve as drain regions (“D”) and the second doped regions 24 serve as source regions (“S”). The drain regions 22 and the source regions 24 can be arranged in an alternating checkerboard pattern in the substrate 20 as shown in FIG. 1.

If the switch is to be a PMOS transistor, then the doped regions 22 and 24 can be p-doped portions in an n-type substrate or well. If the switch is to be a NMOS transistor, then the doped regions 22 and 24 can be n-doped portions in a p-type substrate or well. If the switch is to be an LDMOS transistor, then the drain regions 22 can be n-doped portions in an n-type substrate or well, and the source region 24 can include both highly p-doped and highly n-doped portions in a lightly-p-doped p-body in the n-type substrate or well.

A gate 200 is also formed on the substrate 20. Assuming that the doped regions 22 and 24 are arranged in a checkerboard pattern, the gate can include a first set of parallel gate lines 202 and a second set of parallel gate lines 204. The two sets of gate lines 202 and 204 can intersect to form a rectangular array that surrounds each doped region 22 or 24. The gate lines 202 and 204 are formed of a conductive material 210, such as polysilicon, that is separated from the semiconductor substrate body 26 by a gate insulator layer 212, such as silicon dioxide. An additional insulator layer 214 may be formed over the polysilicon to prevent a short circuit with the first conductive layer 30. Apertures 216 in the additional insulator layer 214 provide electrical contact between the first conductive layer 30 and the source and drain regions 22 and 24 in the substrate. Since the gate lines 202 and 204 extend off to the edges of the active area, the vias for electrical connections to the gate lines can be made near the edge of the switch, away from the interconnects for the source and drain.

Returning to FIG. 1, the first conductive layer 30 includes a plurality of first regions 32 a and a plurality of second regions 32 b. The plurality of first regions 32 a are electrically isolated from the plurality of second regions 32 b. Each region 32 a and 32 b overlies multiple source and drain regions 22 and 24. Although each region 32 a and 32 b is illustrated as overlying an identical sized array of doped regions, this is not required.

Each first region 32 a includes an interconnected conductive sheet 34 a with apertures 36 a. A conductive island 38 a is formed in each aperture 36 a. Similarly, each second region 32 b includes a conductive sheet 34 b with apertures 36 b and conductive islands 38 b formed in the aperture 36 b. Thus, the conductive islands are electrically insulated from the conductive sheets. The sheets 34 a, 34 b can be generally continuous, and the apertures 36 a, 36 b can be periodically spaced across the sheet.

In each first region 32 a, the conductive islands 38 a overlie the source regions 24, whereas the conductive sheet 34 a overlies and interconnects the drain regions 22. In contrast, in each second region 32 b, the conductive islands 38 b overlie the drain regions 22 and the conductive sheet 34 b overlies and interconnects the source regions 24. Thus, the combination of the conductive sheet 34 a and the conductive islands 38 b form a drain electrode, whereas the combination of the conductive sheet 34 b and the conductive islands 34 a form a source electrode.

Many other layouts of the doped regions and the first metal layer 30 are possible. For example, as described below, the doped regions and first conductive layer could be alternating stripes instead of a checkerboard pattern. Optionally, the adjacent portions of the conductive sheets 34 a and 34 b can form interleaved projections that overlie the drain and source regions 22 and 24, respectively. Optionally, conductive sheets 34 a and 34 b can be implemented as alternating stripes, e.g., as shown in FIG. 9.

Referring to FIGS. 1-3, the second conductive layer 40 includes a plurality of first conductive areas 42 a, a plurality of second conductive areas 42 b, a plurality of third conductive areas 44 c and a plurality of fourth conductive areas 42 d. Each plurality of conductive area 42 a, 42 b, 42 c and 42 d is electrically isolated from the other pluralities of conductive area within the second conductive layer 40. Electrical isolation between adjacent conductive areas can be provided by portions of the insulation layer 72. Each conductive area 42 a, 42 b, 42 c and 42 d can be about the same size as an underlying conductive region 32 a or 32 b.

In a first region 41 a of the second conductive layer 40, the plurality of first conductive areas 42 a and the plurality of second conductive areas 42 b are arranged in an alternating pattern, e.g., a checkerboard pattern. Similarly, in a second region 41 b of the second conductive layer 40, the plurality of third conductive areas 42 c and the plurality of fourth conductive areas 42 d are arranged in an alternating pattern, e.g., a checkerboard pattern. For example, each region 41 a or 41 b can include an array of alternating conductive areas 42 a and 42 d or 42 b and 42 c, respectively. Although each region 41 a and 41 b is illustrated as including an identical sized array of conductive areas, this is not required. In addition, although FIG. 1 illustrates only a single first region 41 a and a single second region 41 b, there can be multiple regions 41 a and 41 b themselves arranged in an alternating pattern, e.g., a checkerboard pattern.

The conductive areas 42 a, 42 b, 42 c and 42 d of the second conductive layer 40 are connected by vias 220-226 (illustrated in phantom in FIG. 1) to the conductive islands 38 a and 38 b in the adjacent underlying regions 32 a and 32 b of the first conductive layer 30. For the purpose of clarity, not every via is illustrated. Specifically, the plurality of first areas 42 a of the second conductive layer 40 are electrically coupled to the conductive islands 38 a in the underlying first regions 32 a of the first conductive layer 30 by vias 220. Similarly, the plurality of second areas 42 b of the second conductive layer 40 are electrically coupled to the conductive islands 39 b in the underlying second regions 32 b of the first conductive layer 30 by vias 222. The plurality of third areas 42 c of the second conductive layer 40 are electrically coupled to the conductive islands 38 b in the underlying second regions 32 b of the second conductive layer 30 by vias 224. The plurality of fourth areas 42 d of the second conductive layer 40 are electrically coupled to the conductive islands 38 a in the underlying second regions 32 b of the first conductive layer 30 by vias 222. Thus, in the second metal layer 40, the combination of the first conductive areas 42 a and the fourth conductive areas 42 d forms the source electrode, whereas the combination of the second conductive areas 42 b and the third conductive areas 42 c forms the drain electrode.

Each conductive area 42 a, 42 b, 42 c and 42 d can be a planar layer of a conductive material, such as a metal layer. For example, each conductive area 42 a, 42 b, 42 c and 42 d can be a substantially continuous plane. However, to provide access from the overlying third conductive layer 50 and under-bump metallization 60 to the conductive sheets 34 a and 34 b, each conductive area 42 a, 42 b, 42 c and 42 d can have one or more isolation structures 44 a, 44 b, 44 c and 44 d, respectively.

Referring to FIG. 4, each isolation structure, e.g., isolation structure 44 a, is an aperture 46 in the conductive area 42 a that includes a conductive island or via 48 that is electrically isolated from the surrounding conductive area 42. These isolation structures will be further discussed below.

Optionally, the first metal layer 30 and the second metal layer 40 can be interconnected at their edges. If so, then adjacent portions of the conductive area 42 a, 42 b, 42 c and 42 d can form interleaved projections that overlie the projections from the conductive sheets 34 a and 34 b. In particular, projections from conductive areas 42 a and 42 d would overlie and be connected by vias to projections from conductive sheets 34 b, whereas projections from conductive areas 42 b and 42 c would overlie and be connected by vias to projections from conductive sheets 34 a. Thus, conductive sheets 34 a and conductive areas 42 b and 42 c would form a laterally interconnected drain, whereas conductive sheets 34 b and conductive areas 42 a and 42 d would form a laterally interconnected source. Alternatively, projections can be formed in only one of the metal layers 30, 40.

Returning to FIG. 1, the third conductive layer 50 includes at least one first region 52 a and at least one second region 52 b. The first region 52 a is electrically isolated from the second region 52 b. Each first region 52 a of the third conductive layer 50 overlies a first region 41 a of the second conductive layer 40, and each second region 52 b of the third conductive layer 50 overlies a second region 41 b of the second conductive layer 40. Thus, the first region 52 a will overlie multiple conductive areas 42 a and 42 d, and the second region 52 b will overlie multiple conductive areas 42 b and 42 c. For example, each region 52 a or 52 b can overlie an array of alternating conductive areas 42 a and 42 d or 42 b and 42 c, respectively. Although each region 52 a and 52 b is illustrated overlying an identical sized array of conductive areas, this is not required. In addition, although FIG. 1 illustrates the third conductive layer 50 as including only a single first region 52 a and a single second region 52 b, there can be multiple regions 52 a and 52 b arranged in an alternating pattern, e.g., a checkerboard pattern or a sequence of alternating rows.

Each conductive region 52 a and 52 b can a planar layer of a conductive material, such as a metal layer. For example, each conductive region 52 a,d 52 b can be a substantially continuous plane. However, to provide access from the overlying under-bump metallization 60 to the conductive areas 42 a, 42 b, 42 c and 42 d of the second metal layer 40 and the conductive sheets 34 a and 34 b of the first metal layer 30, each conductive region 52 a, 52 b, can have a number of isolation structures 54 a, 54 b, 54 c and 54 d. As with the second metal layer, each isolation structure 54 a, 54 b, 54 c or 54 d includes an aperture 56 in the conductive area within which is located a conductive island or via 58 that is electrically isolated from the surrounding conductive area. In general, there is at least one isolation structure for each conductive area 42 a, 42 b, 42 c or 42 d of the second metal layer 40 that the conductive region 52 a or 52 b overlies.

The conductive regions 52 a and 52 b of the third conductive layer 50 are connected by vias 230-236 to the conductive sheets 34 a and 34 b in the underlying regions 32 a and 32 b of the first conductive layer 30 and to the conductive areas 42 a, 42 b, 42 c and 42 d of the second conductive layer (although FIG. 1 illustrates one via per connected area or region, there could be more than one). Specifically, the first conductive region 52 a is electrically coupled to the underlying second conductive areas 42 b in the second conductive layer 40 by vias 230. In addition, the first conductive region 52 a is electrically coupled to the conductive sheets 34 a of the underlying first conductive regions 32 a of the first metal layer 30 by vias 232 that pass through the isolation structures 44 a in the first conductive areas 42 a of the second metal layer 40. Similarly, the second conductive region 52 b is electrically coupled to the underlying fourth conductive areas 42 d in the second conductive layer 40 by vias 234, and to the conductive sheets 34 b of the underlying second conductive regions 32 b of the first metal layer 30 by vias 236 that pass through the isolation structures 44 c in the third conductive areas 42 c of the second metal layer 40. Thus, in the third metal layer 50, the first conductive region(s) 52 a is part of the drain electrode, whereas the second conductive region(s) 52 b is part of the source electrode.

At the edge of the first conductive region 52 a that is adjacent the second conductive region 52 b are one or more lateral protrusions 240, such as a plurality of rectangular protrusions. Similarly, at the edge of the second conductive region 52 b that is adjacent the first conductive region 52 a are one or more lateral protrusions 242, such as a plurality of rectangular protrusions. The rectangular protrusions 240, 242 of the two conductive regions 52 a, 52 b areas can interlace in an alternating pattern to form a region of interdigitated protrusions at the common edge of the conductive regions 52 a and 52 b.

As discussed further below, the lateral protrusions 240 of the first conductive region 52 a of the third metal layer can vertically underlie protrusions 252 from a second conductive area 62 b of the UBM layer 60. Electrical coupling between the lateral protrusions 240 of the first conductive region 52 a of the third metal layer 50 and the protrusions 252 from the second conductive area 62 b of the UBM layer 60 can be provided by vias 260. Similarly, the lateral protrusions 242 of the second conductive region 52 b of the third metal layer can vertically underlie protrusions 250 from a first conductive area 62 a of the UBM layer 60. Electrical coupling between the lateral protrusions 242 of the second conductive region 52 b of the third metal layer 50 and the protrusions 250 from the first conductive area 62 a of the UBM layer 60 can be provided by vias 262.

Referring to FIGS. 1, 5 and 6, the UBM layer 60 is similar to the third conductive layer 50, and includes one or more first conductive areas 62 a and one or more second conductive areas 62 b, with the first areas 62 a electrically isolated from the second areas 62 b. The first conductive area 62 a and the second conductive area 62 b can simply be physically separated structures on the top surface of the integrated circuit chip (e.g., separated by an air gap), or an insulation layer can be provided in the lateral space between the two areas 62 a and 62 b.

As best shown in FIG. 6, the UBM layer 60 can include a conductive pad layer 280, such as a metal layer, e.g., aluminum, on which is formed a conductive intermediate layer 282, such as nickel-vanadium alloy. An outer conductive layer, e.g., a copper layer, is then deposited on the intermediate layer. The aluminum layer can be 1 micron thick, and the copper layer can be 0.8 micron or more, e.g., up to 14 microns thick. The intermediate layer 282 provides a diffusion barrier.

In another implementation, the UBM includes a conductive pad layer, such as a metal layer, e.g., titanium. On the titanium layer a thin conductive seed layer, e.g., of copper, is deposited, e.g., by sputtering, and a thick conductive outer layer, e.g., of copper, is deposited, e.g., by plating, on the seed layer. The thick conductive outer layer can be more than 6 microns thick, e.g., more than 9 microns thick, e.g., about 12 to 14 microns thick. The thick copper layer prevents electrical discontinuity from developing due to consumption of the copper layer during formation of the bump.

A metal solder bump 290 is formed on the thick conductive outer layer 286. One metal solder bump 290 can be provided per conductive area 62 a or 62 b, e.g., particularly if the conductive areas 62 a and 62 b are arranged in a checkerboard pattern. Alternatively, more than one metal solder bump 290, e.g., a row of bumps, can be provided per conductive area 62 a or 62 b, e.g., particularly if the conductive areas 62 a and 62 b are arranged in alternating TOWS.

Vias, e.g., vias 270 or 272, between the UBM layer 60 and the third conductive metal layer 50 (particularly the conductive island 58 in the isolation structures), can be provided by apertures in the passivation layer 74, into which at least the contact layer 282 of the UBM layer 60 extends to contact the third conductive metal layer 50. At least some of the vias 270 or 272 are not directly under the solder bump 290.

As noted above, an edge of the first conductive area 62 a adjacent the second conductive area 62 b has one or more lateral protrusions 250, e.g., as a plurality of rectangular protrusions that extended toward the second conductive area 62 b. Similarly, an edge of the second conductive area 62 b adjacent the first conductive area 62 a has one or more lateral protrusions 252, e.g., a plurality of rectangular protrusions that extended toward the first conductive area 62 a. The rectangular protrusions of the two conductive areas can interlace in an alternating pattern to form a region of inter-digited protrusions at the common edge of the conductive areas 62 a and 62 b.

The first conductive area 62 a of the UBM layer 60 may substantially overlap the first conductive region 52 a of the third metal layer 50 except for the extended regions. Similarly, the second conductive region 64 b of the UBM layer 60 may substantially overlap the second conductive area 52 b of the third metal layer 50 except for the extended regions.

As noted above, the lateral protrusions 250 of the first conductive area 62 a of the UBM layer 60 overlap the lateral protrusions 242 of the second conductive region 52 a of the third metal layer 50, and vias 262 provide electrical couplings between the overlapped areas. Similarly, the lateral protrusions 252 of the second conductive area 62 b of the UBM layer 60 overlap the lateral protrusions 240 of the first conductive region 52 a, and vias 260 provide electrical couplings between the overlapped areas. The overlapping protrusions and vias form an “interstitching” structure that electrically couples the first conductive region 52 a of the third metal layer 50 with the second conductive area 62 b of the UBM layer 60, and electrically couples the second conductive region 52 b of the third metal layer 50 with the first conductive region 62 a of the UBM layer 60.

The conductive areas 62 a and 62 b of the UBM 60 are connected by vias 270-276 to the conductive sheets 34 a and 34 b in the regions 32 a and 32 b of the first conductive layer 30 and to the conductive areas 42 a, 42 b, 42 c and 42 d of the second conductive layer that underlie the particular conductive area (although FIG. 1 illustrates one via per connected area or region, there could be more than one). Specifically, the first conductive area 62 a of the UBM layer 60 is electrically coupled to the underlying first conductive areas 42 a in the second conductive layer 40 by vias 270 that pass through the isolation structures 54 a in the first conductive region 52 a of the third metal layer 50. In addition, the first conductive area 62 a of the UBM layer 60 is electrically coupled to the conductive sheets 34 b of the underlying second conductive regions 32 b of the first metal layer 30 by vias 272 that pass through the isolation structures 54 b in the first conductive region 52 a of the third metal layer 50 and through the isolation structures 44 b in the second conductive areas 42 b of the second metal layer 40. Similarly, the second conductive area 62 b of the UBM layer 60 is electrically coupled to the underlying third conductive areas 42 c in the second conductive layer 40 by vias 274 that pass through the isolation structures 54 c in the second conductive region 52 b of the third metal layer 50, and the second conductive area 62 b of the UBM layer 60 is electrically coupled to the conductive sheets 34 a of the underlying first conductive regions 32 a of the first metal layer 30 by vias 276 that pass through the isolation structures 54 d in the second conductive region 52 b of the third metal layer 50 and through the isolation structures 44 d in the fourth conductive areas 42 d of the second metal layer 40. Thus, the first conductive area 62 a of the UBM layer 60 becomes the source electrode, and the second conductive area 62 b of the UBM layer 60 becomes the drain electrode.

In summary, FIG. 1 illustrates an implementation in which the drain regions 22 are electrically coupled to the first conductive region 52 a of the third metal layer 50 and the second conductive area 62 b of the UBM layer 60, the source regions 24 are electrically coupled to the second conductive region 52 b of the third metal layer 50 and the first conductive area 62 a of the UBM layer 60, and third metal layer 50 and the UBM layer 62 are connected by an interstitching that keeps the drain and source electrodes electrically isolated. A schematic circuit diagram of this configuration is illustrated in FIG. 7.

Although FIG. 1 illustrates the UBM layer 60 with just two adjacent conductive areas 62 a and 62 b, the integrated circuit structure can be fabricated with multiple interconnected areas. For example, referring to FIG. 8, the conductive areas 62 a and 62 b can be formed in a checkerboard pattern, with interstitching connecting the second and third conductive layers at the adjacent boarder of each pair of conductive areas. Alternatively, the conductive areas 62 a and 62 b can be arranged in alternating rows, columns, or in some other pattern. This permits the source and drain pads on the top surface of a chip to be arranged in rows, columns, in a checkerboard, or in some other pattern.

With the aforementioned implementation, the integrated circuit structure of the present invention couples the source and drain regions of the distributed transistor to the conductive planes of the UBM layer 60 with short lateral interconnects in the first and second conductive layers. Because the third conductive layer 50 and the UBM layer 60 can be relatively thick, they can carry large amounts of current (in comparison to the buried first and second conductive layers 30 and 40, which should be thinner). In particular, the UBM layer 60 can carry current laterally to vias (e.g., vias that are not directly under the solder bump) with lower resistance than the first and second conductive layers. The planar current flow in the third conductive layer 50 and UBM layer 60 and the short path of direct vertical interconnects reduce the current flow density and resistance of interconnects. The invention therefore reduces power loss of circuits and improves the reliability of circuits and devices. If conducting pads can be placed above the functional area, the invention reduces area needed for providing conducting pads on an IC chip and produces cheaper dies in a smaller package than a traditional IC structure.

FIGS. 9 and 10 illustrate another implementation of an integrated circuit structure 310 that can be used as a power switch. Except as set forth below, the integrated circuit structure of FIGS. 9 and 10 can be constructed similarly to the structure of FIGS. 1-8.

The structure 310 includes a substrate 320, a lowermost first conductive layer 310, a middle second conductive layer 340 over the first conductive layer 320, and a third conductive layer 350 over the second conductive layer 340. In addition, an under-bump metallization (UBM) layer 360 is disposed over the third conductive layer 350 to provide electrical contact for a solder bump 380.

Referring to FIG. 9, the substrate 320 has a number of first doped regions 322 and a number of second doped regions 324 formed in, e.g., implanted into the surface layer of, a semiconductor substrate body, e.g., a silicon body. The first doped regions 322 and second doped regions 324 can be doped regions of a distributed transistor. In the illustrated implementation, the first doped regions 322 serve as drain regions (“D”) and the second doped regions 324 serve as source regions (“S”). The drain regions 322 and the source regions 324 can be arranged in alternating rows as shown in FIG. 9. The gate can include parallel gate lines 328 that run between each pair of adjacent doped region 322 and 324. Since the gate lines 328 extend off to the opposing edges of the active area, the vias for electrical connections to the gate lines can be made near the edge of the switch, away from the interconnects for the source and drain.

The first conductive layer 330 includes a plurality of first regions 332 a and a plurality of second regions 332 b. In each first region 332 a, conductive strips 334 a overlie the source regions 324 and conductive strips 336 a overlie the drain regions 322. In contrast, in each second region 332 b, conductive strips 334 b overlie the drain regions 322 and conductive strips 336 b overlie the source regions 324. Thus, the combination of the conductive strips 334 a and the conductive strips 336 b form a source electrode, whereas the combination of the conductive strips 334 b and the conductive strips 336 a form a drain electrode. Each region 332 a and 332 b overlies multiple source and drain regions 322 and 324, e.g., multiple rows of alternating regions. Adjacent conductive strips are electrically insulated from each other. Although each region 332 a and 332 b is illustrated as overlying an identical sized group of doped regions, this is not required. Optionally, one or both sets of conductive strips within a region can be electrically connected within the first conductive layer. For example, the strips 334 a could extend past the ends of strips 336 a and be connected to a conductive bar extending along one edge of the region 332 a perpendicular to the strips.

The second conductive layer 340 includes a plurality of first conductive areas 342 a and a plurality of second conductive areas 342 b (only one of each conductive area is illustrated). Each plurality of conductive area 342 a, 342 b is electrically isolated from the other plurality of conductive areas within the second conductive layer 340. Each conductive area 342 a, 342 b can be about the same size as an underlying conductive region 332 a or 332 b, and the conductive areas 342 a, 342 b can be arranged in alternating rows.

The conductive areas 342 a of the second conductive layer 40 are connected by vias 338 a to the conductive strips 334 a in the adjacent underlying regions 332 a of the first conductive layer 330. Similarly, the conductive areas 342 b of the second conductive layer 40 are connected by vias 338 b to the conductive strips 334 b in the adjacent underlying regions 332 b of the first conductive layer 330. For the purpose of clarity, not every via is illustrated.

Thus, in the second metal layer 340, the combination of the first conductive areas 342 a forms the source electrode, whereas the combination of the second conductive areas 342 b forms the drain electrode.

Each conductive area 342 a and 342 b can be a planar layer of a conductive material, such as a metal layer. For example, each conductive area 342 a, 342 b can be a substantially continuous plane. However, to provide access from the overlying third conductive layer 350 to the conductive strips that are not connected to the second conductive layer 340, each conductive area 342 a and 342 b can have one or more isolation structures 344 a and 344 b, respectively. Each isolation structure includes an aperture in the conductive area and a conductive island or via in the aperture that is electrically isolated from the surrounding conductive area.

The third conductive layer 350 includes at least one first region 352 a and at least one second region 352 b. The first region 352 a is electrically isolated from the second region 352 b. Each first region 352 a of the third conductive layer 350 overlies a first conductive area 342 a of the second conductive layer 340, and each second region 352 b of the third conductive layer 350 overlies a second conductive area 342 b of the second conductive layer 340.

Each conductive region 352 a and 352 b can a planar layer of a conductive material, such as a metal layer. For example, each conductive region 352 a, 352 b can be a substantially continuous plane. However, to provide access from the overlying under-bump metallization 360 to the conductive areas 342 a, 342 b of the second metal layer 340, each conductive region 352 a, 352 b, can have a number of isolation structures 354 a, 354 b, respectively. As with the second metal layer, each isolation structure 354 a, 354 b includes an aperture 356 in the conductive area within which is located a conductive island or via 358 that is electrically isolated from the surrounding conductive area. However, the isolation structures 354 a, 354 b can be significantly larger than the isolation structures 344 a, 344 b so as to accommodate larger current flow per structure. There can be multiple isolation structures in each conductive region 352 a, 352 b.

The conductive regions 352 a and 352 b of the third conductive layer 50 are connected by vias 382, 384 to the conductive strips 336 a and 336 b in the underlying regions 332 a and 332 b of the first conductive layer 330. Specifically, the first conductive region 352 a is electrically coupled to the conductive strips 336 a of the underlying first conductive regions 332 a of the first metal layer 30 by vias 382 that pass through the isolation structures 344 a in the first conductive areas 342 a of the second metal layer 40. Similarly, the second conductive region 352 b is electrically coupled to the conductive strips 336 b of the underlying first conductive regions 332 b of the first metal layer 30 by vias 384 that pass through the isolation structures 344 b in the second conductive areas 342 b of the second metal layer 340.

Not all vias are illustrated for clarity. Thus, in the third metal layer 350, the first conductive region(s) 352 a is part of the drain electrode, whereas the second conductive region(s) 352 b is part of the source electrode.

The density of vias 338 a, 338 b per unit length of the conductive strips 334 a, 334 b can be greater than the density of vias 382, 384 per unit length of the conductive strips 336 a, 336 b.

At the edge of the first conductive region 352 a that is adjacent the second conductive region 352 b are one or more lateral protrusions 240, such as a plurality of rectangular protrusions. Similarly, at the edge of the second conductive area 342 a that is adjacent the first conductive region 352 a are one or more lateral protrusions 242, such as a plurality of rectangular protrusions. The rectangular protrusions 240, 242 of the two conductive regions 352 a, 352 b areas can interlace in an alternating pattern to form a region of interdigitated protrusions at the common edge of the conductive regions 352 a and 352 b.

The UBM layer 360 includes one or more first conductive areas 362 a and one or more second conductive areas 362 b, with the first areas 362 a electrically isolated from the second areas 362 b. An edge of the first conductive area 362 a adjacent the second conductive area 362 b has one or more lateral protrusions 250, e.g., as a plurality of rectangular protrusions that extended toward the second conductive area 362 b. Similarly, an edge of the second conductive area 362 b adjacent the first conductive area 362 a has one or more lateral protrusions 252, e.g., a plurality of rectangular protrusions that extended toward the first conductive area 362 a. The rectangular protrusions of the two conductive areas can interlace in an alternating pattern to form a region of interdigitated protrusions at the common edge of the conductive areas 362 a and 362 b.

The first conductive area 362 a of the UBM layer 360 can substantially overlap the first conductive region 352 a of the third metal layer 350 except for the extended regions. Similarly, the second conductive region 362 b of the UBM layer 360 can substantially overlap the second conductive area 352 b of the third metal layer 350 except for the extended regions. The lateral protrusions 250 of the first conductive area 362 a of the UBM layer 360 overlap the lateral protrusions 242 of the second conductive region 352 a of the third metal layer 350, and vias 262 provide electrical couplings between the overlapped areas. Similarly, the lateral protrusions 252 of the second conductive area 362 b of the UBM layer 360 overlap the lateral protrusions 240 of the first conductive region 352 a, and vias 260 provide electrical couplings between the overlapped areas. The overlapping protrusions and vias form an “interstitching” structure that electrically couples the first conductive region 352 a of the third metal layer 350 with the second conductive area 362 b of the UBM layer 360, and electrically couples the second conductive region 352 b of the third metal layer 350 with the first conductive region 362 a of the UBM layer 360.

The conductive areas 362 a and 362 b of the UBM 360 are connected by vias 386, 388 to the conductive areas 342 a and 342 b of the second conductive layer 340 that underlie the particular conductive area (although FIG. 1 illustrates two vias per connected area or region, there could be just one or more than two). Specifically, the first conductive area 362 a of the UBM layer 360 is electrically coupled to the underlying first conductive areas 342 a in the second conductive layer 340 by vias 386 that pass through the isolation structures 354 a in the first conductive region 352 a of the third metal layer 350. Similarly, the second conductive area 362 b of the UBM layer 360 is electrically coupled to the underlying second conductive areas 342 b in the second conductive layer 340 by vias 388 that pass through the isolation structures 354 b in the second conductive region 352 b of the third metal layer 350. Thus, the first conductive area 362 a of the UBM layer 360 becomes the source electrode, and the second conductive area 362 b of the UBM layer 360 becomes the drain electrode.

The density of vias 382, 384 can be greater than the density of vias 386, 388. The vias 344 a, 344 b from the third metal layer 350 to the first metal layer 330 can be omitted in regions where the large vias 348 connects the UBM layer 360 and the second metal layer 340.

Optionally, the edges of the second metal layer 340 can be interstitched with the edges of the third metal layer 350. For example, portions of the projections 240 of the first conductive region 352 a in the third metal layer 350 can extend over and be connected by vias to the second conductive area 342 b in the second metal layer 340, and portions of the projections 242 of the second conductive region 352 b in the third metal layer 350 can extend over and be connected by vias to the first conductive area 342 a in the second metal layer 340. Thus, as illustrated in FIG. 9, the projections are formed in only one of the metal layers 340, 350.

The present invention may be implemented to various kinds of IC chips for providing external couplings to the IC chips. Without limiting the scope of the present invention, the implementation of the invention to an IC chip for voltage regulators is illustrated in detail below as an example.

Voltage regulators, such as DC-to-DC converters, are used to provide stable voltage sources for electronic systems. Switching voltage regulators (or simply “switching regulators”) are known to be an efficient type of DC-to-DC converter. A switching regulator generates an output voltage by converting an input DC voltage into a high frequency voltage waveform, and filtering the high frequency voltage waveform to generate the output DC voltage. Specifically, the switching regulator includes a switch for alternately coupling and decoupling an input DC voltage source, such as a battery, to a load, such as an IC chip. An output filter, typically including an inductor and a capacitor that are provided between the input voltage source and the load, filters the output of the switch and thus provides the output DC voltage. A pulse modulator, such as a pulse width modulator or a pulse frequency modulator, typically controls the switch.

Referring to FIG. 11, an implementation of a switching regulator 110 is coupled to a DC input voltage source 112, such as a battery, by an input terminal 120. The switching regulator 110 is also coupled to a load 114, such as an IC chip, by an output terminal 124. The switching regulator 110 serves as a DC-to-DC converter between the input terminal 120 and the output terminal 124. The switching regulator 110 includes a switching circuit 116 that serves as a power switch for alternately coupling and decoupling the input terminal 120 to an intermediate terminal 122. The switching circuit 116 includes a rectifier, such as a switch or diode, coupling the intermediate terminal 122 to ground. Specifically, the switching circuit 116 and the output filter 126 may be configured in a buck converter topology with a first transistor 130 connected between the input terminal 120 and the intermediate terminal 122 and a second transistor 132 connected between ground and the intermediate terminal 122. The first transistor 130 may be a P-type MOS (PMOS) device or N-type LDMOS device, whereas the second transistor 132 may be an N-type MOS (NMOS) device or N-type LDMOS device, and other permutations of PMOS, NMOS, P-type LDMOS and N-type LDMOS devices are possible. The switching regulator 110 may also include an input capacitor 138 connecting the input terminal 122 to ground.

The switching regulator also includes a controller assembly with a pulse modulator 118 for controlling the operation of the switching circuit 116. The pulse modulator 118 causes the switching circuit 116 to generate an intermediate voltage having a rectangular waveform at the intermediate terminal 122. Although the pulse modulator 118 and the switching circuit 116 are illustrated and described below as a pulse width modulator, the invention is also applicable to various pulse frequency modulation schemes.

The intermediate terminal 122 is coupled to the output terminal 124 by an output filter 126. The output filter 126 filters the rectangular waveform of the intermediate voltage at the intermediate terminal 122 into a substantially DC output voltage at the output terminal 124. Specifically, in a buck-converter topology, the output filter 126 includes an inductor 134 connected between the intermediate terminal 122 and the output terminal 124 and a capacitor 136 connected in parallel with the load 114. During a first conduction interval, the voltage source 112 supplies energy to the load 114 and the inductor 134 via the first transistor 130. During a second conduction interval, transistor 132 is closed and the inductor 134 supplies the energy. The resulting output voltage V_(out) is a substantially DC voltage. Although the switching circuit 116 and the output filter 126 are illustrated in a buck converter topology, the invention is also applicable to other switching voltage regulator topologies, such as a boost converter topology, a buck-boost converter topology, or a variety of transformer coupled topologies.

The output voltage is regulated, or maintained at a substantially constant level, by a feedback loop in the controller assembly that includes a feedback circuit 128. The feedback circuit 128 includes circuitry that measures the output voltage and/or the current passing through the intermediate terminal. The measured voltage and current are used to control the pulse modulator 118 so that the output voltage at the output terminal 124 remains substantially constant.

The conductive routings of the present invention can be used in the switching circuit 116 to provide a flip-chip package that includes the switching circuit and provides external couplings. In general, each switch in the switching circuit 116 is fabricated as a distributed array of parallel transistors, and the conductive routing structures discussed above can carry current from the doped regions to the conducting pads on the surface of the chip.

For example, if the second transistor 132 is implemented as an n-channel device, it can include rectangular n-doped source regions 24 and drain regions 22 laid out in a checkerboard pattern in a p-type well or substrate. If the first transistor 130 is implemented as a p-channel device, is can include alternating rectangular p-doped source regions and drain regions in an n-type well or substrate. If the first transistor 130 is implemented as an re-channel device, it can include alternating rectangular n-doped source regions and drain regions in a p-type well or substrate. A grid-like gate may be implemented to separate each pair of source and drain regions. Electrical connection to the gate can be provided at the peripheral edge of the chip.

Although the description above has focused on the use of the electrical routing to opposite sides of a transistor switch (so that one region of the UBM is connected to a source region of a distributed transistor and another region of the UBM is connected to a drain region of a distributed transistor), the routing structure is generally applicable to supply power to any integrated device, particular integrated devices with regular arrays of circuitry needing connection to an input voltage and ground. Thus, one region of the UBM can be electrically connected to an input voltage line of a circuit block and the other region of the UBM can be electrically connected to the ground line of the circuit block. For example, as shown in FIG. 12, the first region of the UBM is connected as V_(in) to a source of a high-side transistor 142 and another region of the UBM is connected as ground to a source of a low-side transistor 144.

Although the various isolation structures are discussed and illustrated as including one conductive island or via, the isolation structures can include multiple vias in parallel. Although the drawings illustrate hemispherical solder bumps 80, 390, other flip-chip interconnects can be used, such as stud bumps or copper pillars, and the solder bumps can solder balls or be formed in other shapes such as, for example, studs or columnar members.

A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Numerous modifications to the configuration of the conductive routings structure will occur to those of ordinary skill in the art. Accordingly, other embodiments are within the scope of the following claims. 

What is claimed is:
 1. An integrated circuit structure comprising: a first conductive layer disposed on a substrate and providing first electrodes and second electrodes for a distributed transistor in the substrate, wherein the first electrodes and the second electrodes are disposed on the substrate in a pattern of alternating rows; a second conductive layer over the first conductive layer, the second conductive layer having a first conductive portion and a second conductive portion electrically isolated from the first conductive portion, wherein the first conductive portion overlies a first plurality of the first electrodes and a first plurality of the second electrodes and the second conductive portion overlies a second plurality of the first electrodes and a second plurality of the second electrodes; a third conductive layer over the second conductive layer, the third conductive layer having a first conductive region and a second conductive region electrically isolated from the first conductive region, the first conductive region substantially located over the first conductive portion and the second conductive region substantially located over the second conductive portion; first conductive vias connecting the first conductive region to the first plurality of the first electrodes through apertures in the first conductive portion and connecting the second conductive region to the second plurality of the second electrodes through apertures in the second conductive portion, the first conductive vias disposed with a first density per unit length along the rows; second conductive vias connecting the first conductive portion to the second plurality of the first electrodes and connecting the second conductive portion to the first plurality of second electrodes, the second conductive vias disposed with a second density per unit length along the rows that is greater than the first density; and a fourth conductive layer over the third conductive layer, the fourth conductive layer having a first conductive area and a second conductive area electrically isolated from the first conductive area, the first conductive area substantially located over the first conductive region and the second conductive area substantially located over the second conductive region.
 2. The integrated circuit structure of claim 1, wherein the first conductive region includes a first protrusion extending toward the second conductive region and over the second conductive portion, and the second conductive region includes a second protrusion extending toward the first conductive region and over the first conductive portion.
 3. The integrated circuit structure of claim 2, wherein the first conductive region and the second conductive region comprise interdigited protrusions, the interdigited protrusions including the first protrusion and the second protrusion.
 4. The integrated circuit structure of claim 2, wherein the first conductive portion and the second conductive portion lack interdigited protrusions.
 5. The integrated circuit structure of claim 1, wherein the fourth conductive layer comprises an under-bump metallization layer.
 6. The integrated circuit structure of claim 1, comprising third conductive vias connecting the first conductive area to the first conductive portion through apertures in the first conductive region and connecting the second conductive area to the second conductive portion through apertures in the second conductive region.
 7. The integrated circuit structure of claim 6, comprising fourth conductive vias connecting the first conductive area to the second conductive region and connecting the second conductive area to the first conductive region.
 8. The integrated circuit structure of claim 7, wherein the first conductive area or the first conductive region includes a protrusion extending toward the second conductive area or second conductive region, respectively, and the fourth conductive vias are in the protrusion.
 9. The integrated circuit structure of claim 7, comprising an outermost passivation layer, and wherein the first conductive vias and the second conductive vias extend through the outermost passivation layer.
 10. An integrated circuit structure comprising: a first conductive layer disposed on a substrate and providing first electrodes and second electrodes for a distributed transistor in the substrate; a second conductive layer over the first conductive layer, the second conductive layer having first conductive portions and second conductive portions electrically isolated from the first conductive portions, the first conductive portions and the second conductive portions arranged in an alternating pattern; a third conductive layer over the second conductive layer, the third conductive layer having a first conductive region and a second conductive region electrically isolated from the first conductive region, the first conductive region located over a first plurality of the first conductive portions and a first plurality of the second conductive portions, and the second conductive region located over a second plurality of the first conductive portions and a second plurality of the second conductive portions; first conductive vias connecting the first conductive region to the first electrodes through apertures in the first plurality of first conductive portions and connecting the second conductive region to the second electrodes through apertures in the second plurality of second conductive portions; second conductive vias connecting the second plurality of first conductive portions to the first electrodes and connecting the first plurality of second conductive portions to the second electrodes; and a fourth conductive layer over the third conductive layer, the fourth conductive layer having a first conductive area and a second conductive area electrically isolated from the first conductive area, the first conductive area substantially located over the first conductive region and the second conductive area substantially located over the second conductive region.
 11. The integrated circuit structure of claim 10, wherein the first conductive region includes a first protrusion extending toward the second conductive region and over the second conductive portion, and the second conductive region includes a second protrusion extending toward the first conductive region and over the first conductive portion.
 12. The integrated circuit structure of claim 11, wherein the first conductive region and the second conductive region comprise interdigited protrusions, the interdigited protrusions including the first protrusion and the second protrusion.
 13. The integrated circuit structure of claim 11, wherein the first conductive portion and the second conductive portion lack interdigited protrusions.
 14. The integrated circuit structure of claim 10, wherein each first conductive portion overlies a plurality of the second electrodes, and each second conductive portion overlies a plurality of the first electrodes.
 15. The integrated circuit structure of claim 14, wherein each first conductive portion overlies exactly one of the first electrodes and each second conductive portion overlies exactly one of the second electrodes.
 16. The integrated circuit structure of claim 10, wherein the first conductive portions and the second conductive portions are arranged in a checkerboard pattern. 